RE: ST2300 Testing and Experimenting
Well, the 3250 didn't get much help from all those fixes I posted 4/30, but I did get a strong suggestion to sleeve the carb on another forum. I picked up a 3/8" barbed brass fitting for PEX tubing from Ho Depot and mounted it in my drill- filed it down on the OD to make it a light press fit in the carb's rotating barrel. Two bucks and two hours later, this brings the bore down to 10mm and now it gets much better fuel draw. I now can fly the plane reliably from a 2/3 fill (18 oz of a 24 oz tank) and am 20 tanks into loving it. Still gets iffy on a long down line or even landing approach in the first 4 minutes of the 10 minute flight. Iffy means if I hear it start to load up I can throttle up and recover.
BLW, I have my 3250 mounted sideways, pitts pipes down, and you were right about idle needle access. I DID need quite a bit of idle needle adjustment as it broke in. Only after that protracted 3 gal break-in was I able to mount the cowl, as I was frequently tweaking the idle needle for the first 3 gallons. Now it idles very nicely. After tuning many engines, I thought this one was untuneable, but a more experienced buddy watched me fly and suggested that the excessively rich idle was carrying so much fuel in the crankcase that the transition and even high end after 30 sec was affected. I was leaving the idle rich for break-in purposes. I sure wish you could pinch-tune the idle, but that does not seem to work for this engine.
So my vote for a balky 2300 (if it works for the 3250, 10mm is plenty for the 2300!) would be to replace the carb with one that has a 10mm airflow bore, or sleeve it the way I did, especially if you have little or no backpressure- i.e. when you are using an aftermarket Pitts Muffler. If you are not sure, and want to go getting all scientific, a manometer is easy to rig up to test the backpressure- just put a T fitting in the exhaust pressure line, and run a 4 foot piece of tubing in a U shape, with a 1 foot drop from the T fitting, then couple of feet going vertically above the fuel tank height. n I lashed mine to a 3' piece of pipe driven in the ground to hold it vertical.
Fill the U with ~2 ft of fuel, so that the U is filled 1 ft per side and fire the engine up. The difference in the two legs of the U when the engine is running ought to be at least 6 inches, better at 12 inches. 12 is equal to about 0.5 psi which I hear is ST's recommendation. I haven't got one of their factory mufflers, so I cannot confirm the "standard" Supertiger mufflers' backpressure.
Now that it's broken in, I just get it primed enough to be "squishy", say 5-7 cranks with the carb covered at full throttle, close the throttle to idle, flip it 7-10 times with no glow plug attached.
Then I hook up the glow, set the throttle up a click or two from dead idle and back flip it to start, i.e. not thru the compression stroke in normal direction, but just backwards enough to hit compression without going past TDC.
It basically backfires itself into starting forward 8/10 times! I had read about this, but never believed MY 3250 would ever be that loose and easy to start. It used to be 50x harder than this to start. The other 1/10 times it starts backwards, and 1/10 times I have to reprime it or it is too hot to restart so easily. Keep the faith is my message here- breakin counts for a lot on these engines in terms of starting and ildle. Burn a couple of gallons or even 4 gallons of 10% before your final verdict. Not such a cheap engine after that $60 in 10% fuel, but not a bad invesment once you are commited to the engine by buying it and cutting your cowl to it, eh?!?!? Besides, if you are a little daring and have a reliable gliding airframe, you can get a FEW minutes of joy in the air after the first gallon....